Spray dryer

ABSTRACT

This invention relates to a method of minimizing the deposit of products on the cylinder wall and their back eddying into the high temperature zone through introducing tangential air currents from the inlets arranged around the discharge end of the cylinder of spray dryer so as to swirl within said cylinder. This invention also comprises an improved spray dryer for carrying out the above mentioned method.

[ 1 July 22,1975

United States Patent [191 Saguchi et al.

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[57] ABSTRACT This invention relates to a method of minimizing thedeposit of products on the cylinder wall and their back eddying into thehigh temperature zone through intro- 48 L ducing tangential air currentsfrom the inlets arranged around the discharge end of the cylinder ofspray 159/4 CC, 4 F 4 K. 4 GC, 4 S, 48 R [56] References Cit d dryer soas to swirl within said cylinder. This invention UNITED STATES PATENTSalso comprises an improved spray dryer for carrying out the abovementioned method.

3 Claims, 1 Drawing Figure l/l9l7 Krauseunmnnum.

PRIMARY HOT MR SOT-GOD'S SECONDARY HOT AIR I50C comm 20-0 (1 PATENTEDJUL 2 2 I975 4 sownou PRIMARY nor AIR sow-some A SECONDARY HOT AIR 150's8 E CODLAIR 20% C ,2 CYCLONE SPRAY DRYER Spray dryer comprising a dryingcylinder provided at one end with a spray nozzle and hot primary airinjecting tube surrounding said nozzle has been known.

ln such a spray dryer, the products tend to deposit on the cylinder walland recycle into the high temperature zone. In order to do away withsuch defects, various methods have been devised, but they all failed.One of the most commonly employed methods is the introduction of the hotsecondary air concurrently to the main flow, but it is not so successfulas expected.

While the inventors of this invention were investigating this problem,they had accidentarilly discovered the solution. According to this, theabove mentioned defects may be effectively overcome by introducingtangential air currents from the inlets arranged arround the dischargeend of the cylinder. Within the cylinder, said air currents spirallyflow along the cylinder wall and envelope completely the main flowconsisting of the particles and hot primary air whereby the deposit ofthe products on the cylinder wall may be completely avoided. As said aircurrents fill the vacant space adjacent the spray zone the back eddyingof the particle may also be effectively avoided.

Finally, said spiral air currents turn their courses and flow back tothe discharge end of the cylinder together with the main flow.

The above mentioned function of the spiral air currents were observedthrough peep holes provided in the cylinder wall with the introductionof paper strips.

lt is to be noted that not whole of the said countercurrents follow theabove mentioned courses, but small portion of said countercurrents flowsback to the discharge end of the cylinder together with the main flowbefore reaching the spray zone.

The substance of this invention will become apparent as this descriptionproceeds in conjunction with the accompanying drawing which shows across sectional view of the spray dryer according to this invention.

1 is drying cylinder. 4 is tube for supplying the solution or suspensionof the material to be dried such as fruit juice. 5 is tube for blowinghot primary air with great speed. Said tube surrounds the tube 4 so asto pulverrize the feed from the tube 4. While flowing through thecylinder 1, particles are dried through intimately mixing with hot air.The completely dried products and remaining air are finally led to thecyclone 2 where they are separated from each other.

In such a spray dryer, some of the particles tends to deposit on thecylinder wall and is overheated there whereby scorching of the particleswill result. Further, some of the particles tends to back eddy into thehigh temperature zone whereby clogging of the spray nozzle oftenresults. In order to overcome said defects, it has been devised tointroduce a large amount of hot secondary air to the spraying zonethrough tube 6, but this method is not so effective as expected.

However, by adopting the method according to this invention, tangentialair currents are introduced from the bustle duct 3 into the dryingcylinder 1 through inlets 7,7',7 arranged around the discharge end ofsaid cylinder.

Said countercurrents flow spirally along the cylinder wall toward thespray zone while completely envelope the main flow F consisting of theparticles and primary air whereby the deposit of particles on thecylinder wall may be effectively avoided.

After said spiral air currents fill the vacant space near the sprayzone, they flow back to the discharge end of the cylinder together withthe main flow F. In virtue of this action, the back eddying of theproducts into the high temperature zone may also be avoided.

It is to be noted not whole of the spiral air currents follow the abovementioned courses, but small portion thereof flows back to the dischargeend of the cylinder together with the main flow F as shown by arrows abefore reaching the spray zone.

Now, in order to understand the merits of this invention, data obtainedby experiments are given below.

The diameter of the dryin c linder g y 3500mm The length of the dryincylinder The pressure at the disc arge end of the cylinder The number ofinlets for introducing -3mm water column As is obvious from the above,the rate of evaporation per volume of the cylinder according to thisinvention is about SSKg/m which is more than ten times larger than thehitherto known rates.

This invention is also applicable to vacuum spray evaporator, flashdryer, spray cooling granulator or the like. Further, drying cylindermay be vertical, horizontal or even tilted.

What we claim is:

1. A spray dryer comprising: a hollow cylinder forming a drying chamberhaving a first inlet end and a second outlet end, a liquid supply tubehaving a discharge end disposed axially within said inlet end of saidchamher, a first primary hot air supply tube concentrically disposedwith respect to said liquid supply tube, and terminating in a commontransversely plane therewith, a second hot air supply tube connectedwith said inlet end of said cylinder to provide a cylindrical column ofair completely surrounding said first hot air supply tube in the area ofsaid common plane, a third air supply tube having means forcommunicating with the interior of said outlet end of said chamber andintroducing at least one spiral air current moving tangentially withrespect to the inner surface of said cylinder and in a longitudinaldirection toward said inlet end; whereby said spiral air current forms amoving curtain preventing hot dry particles outwardly penetrating saidcylindrical column of air from adhering to the inner surface of saidcylinder, said spiral air current mixing with said cylindrical column ofhot air along the axis of said cylinder to lower the effectivetemperature thereof at the outlet end of said cylinder.

2. Structure in accordance with claim 1, in which the volume flow ratioexisting between said first hot air supply tube, said second hot airsupply tube, and said third air supply tube is in the order of l:l:0.l.

3. Structure in accordance with claim 2, in which said first air supplytube supplies air at approximately 500-600C. and said third air supplytube supplies air

1. A SPRAY DRYER COMPRISING: A HOLLOW CYLINDER FORMING A DRYER CHAMBER HAVING A FIRST INLET END AND A SECOND OUTLET END, A LIQUID SUPPLY TUBE HAVING A DISCHARGE END DISPOSED AXIALLY WITHIN SAID INLET END OF SAID CHAMBER, A FIRST PRIMARY HOT AIR SUPPLY CONCENTRICALLY DISPOSED WITH RESPECT TO SAID LIQUID SUPPLY TUBE, AND TERMINATING IN A COMMON TRANSVERSELY PLANE THEREWITH, A SECOND HOT AIR SUPPLY TUBE CONNECTED WITH SAID INLET END OF SAID CYLINDER TO PROVIDE A CYLINDRICAL COLUMN OF AIR COMPLETELY SURROUNDING SAID FIRST HOT AIR SUPPLY TUBE IN THE AREA OF SAID COMMON PLANE, A THIRD AIR SUPPLY TUBE HAVING MEANS FOR COMMUNICATING WITH THE INTERIOR OF SAID OUTLET END OF SAID CHAMBER AND INTRODUCING AT LEAST ONE SPIRAL AIR CURRENT MOVING TANGENTIALLY WITH RESPECT TO THE INNER SURFACE OF SAID CYLINDER AND IN A LONGITUDINAL DIRECTION TOWARD SAID INLET END, WHEREBY SAID SPIRAL AIR CURRENT FORMS A MOVING CURTAIN PREVENTING HOT DRY PARTICLES OUTWARDLY PENETRATING SAID CYLINDRICAL COLUMN OF AIR FROM ADHERING TO THE INNER SURFACE OF SAID CYLINDER, SAID SPIRAL AIR CURRENT MIXING WITH SAID CYLINDRICAL COLUMN OF HOT AIR ALONG THE AXIS OF SAID CYLINDER TO LOWER THE EFFECTIVE TEMPERATURE THEREOF AT THE OUTLET END OF SAID CYLINDER.
 2. Structure in accordance with claim 1, in which the volume flow ratio existing between said first hot air supply tube, said second hot air supply tube, and said third air supply tube is in the order of 1:1:0.1.
 3. Structure in accordance with claim 2, in which said first air supply tube supplies air at appRoximately 500*-600*C. and said third air supply tube supplies air at approximately 20*C. 